1. Field of Invention
The present invention relates to a movement conversion device for motor-driven power tools such as, e.g. compass and saber saws, for converting a rotational movement into a linear reciprocating movement and including an axially reciprocating spindle provided with a connecting link guide, a motor-driven driving gear, and eccentric member displaceably supported on the driving gear and extending into the connecting link guide for converting the rotational movement of the driving gear into the reciprocating movement of the reciprocating spindle, the eccentric member having, for changing a length of the reciprocating stroke of the reciprocating movement and for changing a load torque acting on the driving gear, a first position with respect to a rotational axis of the driving gear in which a distance between the eccentric member and the rotational axis is greater than in at least one second position of the eccentric member. The present invention also relates to a hand-held power tool including the inventive movement conversion device.
2. Description of the Prior Art
With movement conversion devices of the type described above, there exists a possibility to adapt the tools referred to above to different uses by changing the eccentricity of the eccentric member, i.e., the distance between the eccentric member and the rotational axis of the driving gear. e.g., during the treatment of soft materials, the second position, which is characterized by a greater distance of the eccentric member from the rotational axis, can be selected to provide for a maximal stroke length and, thereby, for a more rapid operation of the power tool.
For treating hard materials, the maximal stroke length can cause overloading of the drive motor. In this case, the first position of the eccentric member is selected, in which the distance from the eccentric member to the rotational axis is small and with which, a greater output of the tool is achieved. In the first position of the eccentric member, the stroke length, along which the reciprocating spindle reciprocates, is adjusted to a minimum so that the motor is not overloaded even at relatively large press-on forces being applied to the treated material.
German Publication DE 36 33 888 discloses a movement conversion device for a compass saw having different stroke lengths for two rotational directions of the drive motor. In the disclosed device, the eccentric disc which is pivotally supported on the driving gear between two stops, is provided with an eccentric pin. When the driving gear rotates counterclockwise, the eccentric disc abuts the first stop. When the driving gear rotates clockwise, the eccentric disc abuts the second stop. The distance between the eccentric pin which is provided on the eccentric disc, and the rotational axis of the driving gear and, thereby, the stoke length or the load applied to the motor changes between the two positions of the eccentric disc.
The drawback of the known conversion device consists in that it can be used in hand-held tools in which the driving gear rotates in both directions. In addition, during a single operational step, the prevailing conditions can change, e.g., when working a material with a variable hardness, or with different possibilities for applying a press-on force by the tool operator. As a result, it might be necessary to change the stoke length several times during a single operational step. In this case, the process should be interrupted, which leads to loss of time. In addition, with materials having a variable hardness, an erroneous position can be set which would result, at least for a short time, in a high load being applied to the motor.
Accordingly, an object of the present invention is to provide a movement conversion device in which the above-discussed drawbacks of the prior art are eliminated.
Another object of the present invention is to provide a movement conversion device that would increase the output of the tool.